Billy Costigan

Billy Costigan (1974-2006) was a Massachusetts State Police trooper. In 2006, he was assigned to infiltrate Francis Costello's Irish Mob, but he was killed by corrupt policeman Colin Sullivan.

Biography
Billy Costigan was born in South Boston, Boston, Massachusetts in 1974 to a family of Irish descent. He had family ties to organized crime; his uncle, Jackie Costigan (whose legitimate job was a carpet layer for Jordan Marsh), was a small-time bookmaker in Somerville who was murdered by a man named Nicastro in 1995. His other uncle, Tommy Costigan, was arrested for selling illegal guns to federal officers. Only his father, who worked as an airport baggage handler, was not a criminal; even a relative of his, who was a Catholic priest, allegedly married a 12-year-old boy and lived with him in Thailand. Costigan's parents later divorced, and he lived two lives: one as an upper-middle-class boy on the North Shore with his mother, and another as a lower-class boy in the "Southie" projects with his father. Costigan decided to break with his family's past and join the Massachusetts State Police.

State trooper
In 2006, Costigan graduated from the police academy, and he was recruited by Captain Oliver C. Queenan and Staff Sergeant Sean Dignam to go undercover, as his family ties to crime made him a perfect infiltrator. After his mother's funeral, he was left with no family, so he had the ability to reinvent himself for his operation.

Undercover work
Because the police could not conceal the fact that he was a trainee, they had him charged with assault and battery, told him to submit a guilty plea, to serve some time in jail, go on probation, and see a court-ordered psychiatrist. After his release from jail, Costigan made contact with his cousin, Sean Costigan, a local drug dealer, and he met Arnold French at a bar after getting into a fight with a patron. Costigan later beat down two Patriarca crime family enforcers at a luncheonette, and he gained the attention of Costello, who hired Costigan into his organization. During his infiltration, Costigan began a romance with his psychiatrist, Madolyn Madden, who was also in a relationship with corrupt policeman Colin Sullivan.

Costigan later discovered that Costello was meeting with the police's mole at a porn theater, and Costigan chased the mole through Chinatown, although he failed to catch him. Costigan later met with Queenan on the roof of a building, but Sullivan, who knew that it was Costigan who had chased him, had Queenan tailed. The Irish mobsters succeeded in killing Queenan, but not Costigan, who pretended that he had come to join the mobsters. Using Queenan's phone, Sullivan reached Costigan, who refused to abort his mission. With Costigan's help, Sullivan tracked down Costello to a cocaine drop-off at the Sheffield Warehouse, and Costello was killed by Sullivan (who was concerned that Costello's status as an FBI informant would threaten his security). Costigan then came to Sullivan for the restoration of his true identity and to finish his mission, but he found an envelope from Costello on Sullivan's desk, so Costigan, realizing that Sullivan was the mole, fled. Sullivan retaliated by erasing Costigan's records from the police computer system.

Death
Later, Costigan told Sullivan that Costello had recorded both of their conversations, and the two of them decided to meet at the building where Queenan died in order to discuss Costigan's intention to implicate Sullivan with the recordings. Costigan caught Sullivan off-guard and handcuffed him, and Trooper Anthony Brown appeared on the roof as well, drawing his gun on Costigan (not knowing that Sullivan was a mole). Costigan led Sullivan to the elevator, holding him hostage, but, when the elevator reached the ground floor, corrupt cop James Barrigan shot Costigan, and then killed Brown. Sullivan then killed Barrigan to prevent him from being a liability. Sullivan went on to name Barrigan as the only mole in the police, and he had Costigan posthumously decorated with the Medal of Merit.